This kind of fan is known, for example, from EP 1 091 171 A1. This document describes a fan burner that can generate a homogeneous air flow. The fan burner comprises a fan housing having a spiral-shaped channel and an approximately perpendicular deflector making it possible to mount a burner housing at the aperture of the spiral-shaped channel lateral to the fan housing. The burner housing is located on the same side of the fan casing as an external drive for a radial impeller of the fan. Due to the deflector, which is turned towards the side of the electric motor, the burner is seated in the free space above the electric motor of the fan, thus making it possible to minimize the overall size of the device.
U.S. Pat. No. 5,839,891 describes a gas burner having an air blower and a device to feed in combustion gas at the outflow side of the air blower. The air blower itself is made up of a spiral-shaped blower housing having an external drive motor, the aperture of the blower housing extending substantially tangential to the air blower. A somewhat protruding device for generating the combustible gas/air mixture is produced thereby, as can be seen from FIG. 1 of this document.
US 2005/0178344 A1 reveals a fan for a gas burner system in which the aperture of the fan housing is deflected by approximately 90° in a similar way like the first document described above, and directly connected to a hot-water boiler. The fan described in this patent application, is fed directly with combustion gas into the fan housing so that the gas/air mixture is already produced in the fan housing. This holds the risk of a combustible gas being formed in the interior of the fan which could ignite due to electrostatic charges. To prevent the gas/air mixture from igniting, conductive material is to be used in the manufacture of the fan housing. In this context, the US patent application describes that the fan housing is either deep-drawn from metal or alternatively made of plastics. If plastics are used, however, only plastics having anti-static properties should be used for both the fan housing as well as the impeller to prevent ignition of the gas/air mixture.
In common gas burner systems, the two basic options are to add the gas either before or after the fan. If the gas is added before the fan, sealing the fan housing becomes particularly critical in order to prevent any leakage of the combustible gas/air mixture. For other types of fans as well, the same efforts are made to design the housing as airproof as possible to prevent any loss of pressure due to leakage flows.
In common fans for gas burner systems, the drive motor of the impeller is always disposed outside of the fan housing. In this arrangement, the motor shaft that is led into the fan housing has to be sealed gas proof against the housing. In accordance with the prior art where the drive motors of the fans are flexibly supported the seal is particularly crucial. The shaft seal required therefor causes friction that puts load on the drive motor.
In practice, the drive motor is decoupled by means of elastic elements from the housing-half on which it is mounted so as to prevent motor vibrations from being transmitted to the gas burner system and thus to ensure that its operation is as noise-free as possible. This elastic support of the drive motor makes it more difficult to seal the motor shaft and the fan housing.
Further prior art that describes fans for gas burner systems can be found, for example, in DE 100 15 399 A1, DE 44 43 045 A1, GB 304,851 and U.S. Pat. No. 2,456,930.
Based on this prior art, an object of the present invention is to provide a fan for a gas burner system that is compact, that can be variably mounted, that can be manufactured at low cost and that does not entail the risk of the gas/air mixture self-igniting.